Network controlling circuits



Dec. 25, 1923. 1,47%,458

D. SMITH NETWORK CONTROLLING CIRCUITS Filed Aug. 24'. 1921 INVENTOR Wgx ATTORNEY Patented Bec. 25, 1923.

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ra` ericae DCN SMITH, 0F SAN FRANCISCO, CALIFORNIA, ASSIGNOR TO AMERICAN TELEPHONE AND TELEGRAPH COMPANY, A COR-PCRATON OF NEW YORK.

NETWORK CONTROLLING CIRCUITS.

Application filed August 24, 1921.

i cur-wire transmission element such as a I epeater station, or a radio station, it somees occurs that the trunk extending trom switching otlice to the repeater or radio sta tion will be so short that ditliculty rwill be encountered in balancing the transmitting f" receiving channelsr ot the repeater or station. Where a trunk is electrically the impedance 'ot the terminal apatns connected to the trunk at the switchstation does not materially aiiect the balance at the repeater or radio station, but where the trunk is short, the impedance of the trunk circuit as seen trom the radio or repeater station will vary considerably with the character of the terminal apparatus. Ttc or" the principal objects of this ini to produce a circuit arrangement whereby the ditiiculties due to balance in circuits or this character may be eliminated.

This object, as well as other objects ot the invention, may be attained by means of the arrangements set forth inthe following description and illustrated in the accompanying drawing, the figure ot which shows one toi-m ot' circuit arrangement embodying the invention.

Referring to the ligure, a radio station is illustrated in which a transmitting antenna Tik and receiving antenna RA are associated with the trunk T leading to a central switching otiice. The antenna RA is associated with the trunk T through a receiving channel RL, including radio receiving apparatus conventionally indicated at RR. Similarly, the transmitting antenna sensi No. 495,082.

TA is associated with the trunk T through a transmitting channel TL including radio transmitting` apparatus conventionally indicated at RT.

Tn order that the transmitting channel TL and the receiving channel RL may be substantially conjugate, these channels are connected to the trunk T through the usual type of hybrid coil 10, and a network N is associated with the terminals of the hybrid coil opposite to the terminals connected to the trunk. The network N is designed so as to present an impedance equal to that ot the trunk T plus a cord circuit and a subscribers line of average length, and arrangements are provided at the opposite terminal ot the trunk to maintain the impedance oi the trunk, as viewed from the hybrid coil, substantially equal to that of the network N under all service conditions.

F or this purpose an auxiliary network N is associated with the end ot the trunk T terminating in the central switching othce, the impedance ot this network being equal to that of a cord circuit plus a subscribers line of average length. The network N is arranged so that it will be associated with the trunk T at all times except when a connectionis established through the cord circuit over a subscribers line, and the subscriber has answered by taking his receiver olf the switchhook. This result is accomplished by bridging the network across the end of the trunk over two independent pairs of conductors, one pair 11 leading to the trunk over contacts otl the terminal jack J of the trunk, and the other pair 12 leading to the trunk over contacts controlled by a relay 13, which responds when the subscriber has his receiver removed trom the switchhook.

C indicates the usual type of operators cord circuit for establishing connections at a central otice, this cord circuit terminating in a plug P adapted to cooperate with the jack J of the trunk at one end, and terminating at the other end in a plug P adapted to coperate with the jack J connected with a subscribers line L. The cord circuit is provided with a relay 14 through which battery current is supplied to the subscribers line, said relay controlling the usual super- 'ing key MK, which when in normal position,

bridges the operators receiver 17 across thev trunk independently of the remainder of the set and maintains a short circuit closed about the terminals of the transmitter 18.

WY hen the key MK is actuated the receiverY 17 is connected across one winding of the.

transformer and the transmitter 18 is rendered operative by opening the short circuit about its terminals. l/Vith the key MK actuated the despatch operator is enabled to both talk and listen over the trunk.

Further details of the apparatus will be clear from a description of the operation. Under normal conditions the balance is maintained between the network N and the trunk T by reason ot' the fact the network NV is connected to the end of the trunk. Should a call come in from the radio station to the central otiice the drop 1,6 would be actuated in a well known manner and the operator would insert the plug P of the cord C into the ljack J, thereby disconnecting the drop 16 and substituting the supervisory drop 15 ot the cord circuit. The

insertion ot' the plug P in the jack J. also disconnects the connections 11 of the nets. work ig from the trunk, butan independent connection over conductors 12 still remains between the network l and the trunk T.

Having ascertained the line to which connection is desired the operator inserts the Vplug P in the jack J of thevline L, leading When the called subscriber answers by removing the receiver from thel switchhook the relay 14 is energized, thereby opening the circuit oif the supervisory lamp 15 and completingva circuit, Jfor the relay 13 which opens the conductors 12 from the. network N to the trunk T. This operation amounts to substituting the subscribeids line and cord circuit for. the network N and consequently the balance is still maintained at the radio station. The despatch o-perator, by means of the set O, may monitor the connection thus established without talking or by throwing ythe monitoring key MK'may both talk and listen on the. connection thus established. Should the operator at any A drop 15 is connected with the time withdraw either the plug P or the plug P from the corresponding jack the network N will at once be connected to the trunk T to maintain the balance. At the termination of the conversatiom the connection is taken down in the usual mannerY in response to the supervisory signal and at once. switched into operator completes the call to the radio' station by inserting the plug P in the jack J the conductors 11 are opened and the network is disconnected, the impedance of the cord` circuit C and ofthe line 11 being substituted for the impedance of the network N so that a balance isA still maintained.

It will be obvious that the general principles herein disclosed may be embodied in many other organizations widely dili'erent .from those illustrated without departing from the spirit of the invention as defined in the following claims. I

What is claimedl is:

1.. Ijn aA signaling system, al trunk circuit of such length that its impedance is not independent of terminal'` Y apparatus connected to one endg of' said trunk circuit, transmitting and receiving channels connected to theA other end of the trunk circuit, a network for balancing said trunkcircuit, said networkhaving an impedance equal to the'iinpedance of the trunk circuit as 1nodilied by the average impedance of various types of terminal apparatus which may be connected to; the trunkcircuit, and a ynetl workconnectedto the other end of the Vtrunk cir-cuit, said network having an impedance simulating that off' the average terminal apparatus co nnected` to the trunk.

2. In a signaling system, a trunk circuit 1 of such length that lits impedance i's not independent 'of terminal apparatus connected to one, end of said; trunk circuit, transmittingV and'V receiving channels connected to the other end of the trunk circuit, va network for balancing saidtrunk circuit, said network having ani'mpedance equal'to Vthe impedance ofthe trunkfcircuit as vmoditied by the average impedance of various typesI of' terminal apparatus which may be Y connected tothe trunk circuit, a network connected', to tl'1 ef V other end; of the trunk circuit,l said, network having an impedance simulating that. ofv the: average, terminal apparatus connected to the trunk, and

means for disconnecting said last mentioned network when terminal apparatus is associatedwith the trunk.

3. In a signaling system, la trunk circuit of'such length that its impedance is not independent or" terminal apparatus connected thereto, means to associate any one of a plurality of transmission lines with one end of said trunk, a transmitting and receiving channel associated' with the opposite end ot said trunk, a network for balancing said trunk at said opposite end, said network having impedance equal to that of the trunk as modiiied by the impedance of the average transmission line connected to the trunk, and a network normally associated with the end oi' the trunk with which the transmission lines are connected, said network simulating the impedance of the average transmission line.

t. ln a signaling system, a trunk circuit of such length that its impedance is not independent of terminal apparatus connected thereto, means to associate any one oit a plurality ot transmission lines with one endL of said trunk, a transmitting and receiving channel associated with the opposite end of said trunk, a network for balancing said trunk at said opposite end, said network having impedance equal to that of the trunk as modified by the impedance ot the average transmission line connected to the trunk, a network normally associated with the end oi' the trunk with which transmis` sion lines are connected, said network simulating the impedance orP the average transmission line,` and means to disconnect said last mentioned network when a transmission line is associated with the trunk.

5. In a signaling system, a switching station at which transmission lines terminate, a translating station at which four-wire transmission apparatus is provided, a trunk extending from said switching station to said translating station having a length such that the impedance of the trunk is not independent of the terminal apparatus assoA ciated therewith, transmitting and receiving channels associated with said trunk at said translating station, and a network for balancing said trunk at said translating station, said network having an impedance equal to that o' the trunk as modiiied by the impedance oi the average transmission line terminating at said switching station, and a network associated with the end of the trunk at said switching station, said network having an impedance equal to that of the average transmission line terminating at said switching station.

6. In a signaling system, a switching station at which transmission lines terminate, a translating station at which four-wire transmission apparatus is provided, a trunk extending from said switching station to said translating station having a length such that the impedance ot the'trunk is not independent o'i the terminal apparatus associated therewith, transmitting and receiving channels associated with said trunk at said translating station, and a network for balancing said trunk at said translating station, said network having an impedance equal to that of the trunk as modified by the impedance of the average transmission line terminating at said switching station, a network associated with the end oi' the trunk at said switching station, said network having an impedance equal to that of the average transmission line terminating at said switching station, and means tordisconnecting said last mentioned network when a connection is established to said trunk over a transmission line.

7. ln a signaling system, a switching sta` tion at which transmission lines terminate, a translating station at which tour-wire apparatus is located, a trunk extending 'from said switching staticn to said translating station, the length et said trunk being such that its impedance is not independent ot terminal apparatus associated therewith, link circuits at said switching station for interconnecting said trunk with any one ot' a plurality oi transmission lines, transmitting and receiving channels at said translating station associated with said trunk, a network at said translating station for simulating the impedance of said trunk as inodied by the impedance of a link circuit and the average impedance of a transmission circuit terminating at the said switchii station, a network at said switching station normally associated with said trunk and lila-ving an impedance simulating that of a link circuit, as modiiied by the average impedance oi3 a transmission line terminating at said station.

8. In a signaling system, a switching station at which transmission lines terminate, a translating station at which 'tour-wire apparatus is located, a trunk extending from said switching station to said translating station, the length of said trunk being such that its impedance is not independent oit terminal apparatus associated therewith, link circuits at said switching station for interconnecting said trunk with any one of a plurality of transmission lines, transmitting and receiving channels at sai-d translating station associated with said trunk, a network at said translating station for simulating the impedance of said trunk as modified by the impedance of a link circuit and the average impedance of a trans` mission circuit terminating at the switching station, a network at said switching station normally associated with said trunk and having an impedance simulating that of a link circuit as modified by the impedanceA of the average transmission line terminating at said sta-tion, and means for disconnecting said last mentioned network when a connection is completed over a transmission line to said trunk through said link circuit.

9. In a signaling system,'a switching station at which transmission linesterminate, a translating station at which 'tour-wire apparatus is located, a trunk extending from said switching station to said translating station, the length of said trunk being such that its impedance is not independent of terminal apparatus associated therewith, link circuits at said switching station for ini terconnecting said trunk with any one of a plurality of transmission lines, transmitting and receiving channels at said translating station associated with said trunk, a network at said translating station for simulating the impedance of said trunk as modified by the impedance oi' a link circuit and the average impedance of a transmission circuit terminating at the said switching station, a network'at said switching station normally associated with said trunk and having an impedance simulating that of a link circuit as modiiied by the Vaverage transmission line terminating at said station, and means associated with said link circuit and responsive to the completion of a connection over a subscribers line to said trunk through said link circuit for disconnecting said last mentioned network.

l0. ln a signaling system, a central switching station, transmission lines terminatingr-thereat, a translating station at which four-wire transmission elements are located, a trunk extending from said switching station to said translating station having a length such that its impedance is not independent of the terminal apparatus connected thereto, a cord circuit for completing connections between said trunk and any of said transmission lines, a transmittinfr and receiving channel associated with sai. trunk at said translating station, a network at said translating station for balancing said trunk, said network having an impedance simulating the impedance of the trunk as siinulatin 0f modiiied by the impedance of said circuit and the impedanceof the average transmission line terminating at said switching oftice, a network at said switching oiiice Jfor simulating the impedance of a cord circuit as modified by the average'impedance of a transmission line terminating at said otiice, and connections between said network and said truiikijointly controlled by the con-v nection of the cord circuit with the trunk, and bythe establishment ot' a connection over a subscribers line and arcord circuit. ll. ln a signaling system, a central switching station, transmission lines terminating thereat, a translating station at which 'four-wire transmission elements are located, a trunk extendin from said switching station to said trans ating station hava length such that its impedance is not independent of the terminal apparatus connected thereto, a cord circuit for completing connections between said trunk and any of said transmission lines, a transmitting and receiving channel associated with said trunk at saidY translating station, a network at said translating station for balancing said trunk, said network having an impedance ,g the impedance of the trunk as modified by the impedance of the cord circuit aiid the impedance of the average transmission line terminating at said switching oiiice, a network at said switching oiiice'ior simulating the impedance of a cord circuit as modifiedV by tlieaverage impedance of a transmission line terminating at'said oiiice,

connections from said network to the trunk,-y

means to open said connections when the cord circuit isassociated with the trunk,

independent connections from said networkY transmission line and the circuit ofthe transmission line is completed.

In testimony whereof, I have signed my name to this specification this 14th day of August, 1921. Y Y Y DON SMITH, 

